如何使用 DateComponentsFormatter 将日期显示为“今天”或“昨天”？

Question

我在我的项目中使用 swift，我想显示这样的特定日期：5 天前或 5 个月前或... 我正在使用 DateComponentsFormatter，它运行良好，但问题是我想在 1 天前显示“昨天”或在 3 秒前显示“今天”。我怎样才能做到这一点？我可以使用 DateComponentsFormatter 解决这个问题吗？这是我的代码：

func shortDate(_ local: LocaleIdentifier = .fa) -> String {
    
    let now = Date()
    let date = self

    let formatter = DateComponentsFormatter()
    formatter.calendar?.locale = Locale(identifier: local.rawValue)
    formatter.unitsStyle = .full
    formatter.maximumUnitCount = 1
    formatter.allowedUnits = [.year, .month, .day, .hour, .minute, .second]

    guard let timeString = formatter.string(from: date, to: now) else {
         return ""
    }

    return String(format: "Ago".localized, timeString)
}

Answer 1

对于 iOS 13 或更高版本，您可以使用 RelativeDateTimeFormatter

let relativeDateTimeFormatter = RelativeDateTimeFormatter()
relativeDateTimeFormatter.dateTimeStyle = .named
relativeDateTimeFormatter.unitsStyle = .full
let date = Date.init(timeIntervalSinceNow: -60*60*24)
relativeDateTimeFormatter.string(for: date)  // "yesterday"

编辑/更新：

如果您想支持 iOS 11，您需要实现自己的相对日期格式化程序。您可以使用 Calendar 方法 isDateInToday 和 isDateInYesterday 将相对日期格式化程序与日期组件格式化程序结合起来。请注意，无需检查在日期组件格式化程序中设置单个单位的时间间隔，您可以设置日期组件格式化程序的允许单位，只需确保按照所需的优先级设置它们即可：

// 这样可以避免每次调用 relativeDateFormatted 属性时都创建格式化程序

extension Formatter {
    static let dateComponents: DateComponentsFormatter = {
        let dateComponentsFormatter = DateComponentsFormatter()
        dateComponentsFormatter.allowedUnits = [.day, .month, .year]  // check the order of the units it does matter when allowing only 1 unit to be displayed
        dateComponentsFormatter.maximumUnitCount = 1
        dateComponentsFormatter.unitsStyle = .full
        return dateComponentsFormatter
    }()
    static let relativeDate: DateFormatter = {
        let dateFormatter = DateFormatter()
        dateFormatter.doesRelativeDateFormatting = true
        dateFormatter.timeStyle = .none
        dateFormatter.dateStyle = .medium
        return dateFormatter
    }()
}

---

extension Date {
    var relativeDateFormatted: String {
        Calendar.current.isDateInToday(self) || Calendar.current.isDateInYesterday(self) ?
        Formatter.relativeDate.string(from: self) :
        Formatter.dateComponents.string(from: self, to:  Date()) ?? "" 
    }
}

---

游乐场测试：

let date1 = DateComponents(calendar: .current, year: 2020, month: 9, day: 4, hour: 5).date!
let date2 = DateComponents(calendar: .current, year: 2020, month: 9, day: 3, hour: 23, minute: 50).date!
let date3 = DateComponents(calendar: .current, year: 2020, month: 8, day: 25, hour: 10).date!
let date4 = DateComponents(calendar: .current, year: 2020, month: 8, day: 3).date!
let date5 = DateComponents(calendar: .current, year: 2019, month: 8, day: 27).date!

date1.relativeDateFormatted  // "Today"
date2.relativeDateFormatted  // "Yesterday"
date3.relativeDateFormatted  // "10 days"
date4.relativeDateFormatted  // "1 month"
date5.relativeDateFormatted  // "1 year"

Answer 2

您正在寻找 DateFormatter 的 doesRelativeDateFormatting 属性。

Answer 3

我认为，我必须同时使用 DateComponentsFormatter 超过 1 天，并使用 DateFormatter 来显示 Today(day=0) 和 Yesterday(day=1) 来解决我的问题。 我找到了我的答案here。

但我把代码做得更好一点，这是我的代码：

var calendar = Calendar.current
calendar.locale = Locale(identifier: local.rawValue)
    
let componentFormatter = DateComponentsFormatter()
componentFormatter.calendar = calendar
componentFormatter.unitsStyle = .full
componentFormatter.maximumUnitCount = 1

let interval = Calendar.current.dateComponents([.year, .month, .day], from: self, to: Date())
    
if let year = interval.year, year > 0 {
    componentFormatter.allowedUnits = .year
} else if let month = interval.month, month > 0 {
    componentFormatter.allowedUnits = .month
} else if let day = interval.day, day > 1 {
    componentFormatter.allowedUnits = .day
} else { // if let day = interval.day, day == 0 || day == 1 for Today or Yesterday

    let formatter = DateFormatter()
    formatter.doesRelativeDateFormatting = true
    formatter.calendar.locale = Locale(identifier: local.rawValue)
    formatter.timeStyle = .none
    formatter.dateStyle = .medium

    return formatter.string(from: self)
}

guard let timeString = componentFormatter.string(from: self, to: Date()) else {
        return ""
}
return String(format: "Ago".localized, timeString)